The invention pertains to methods and devices for automatically switching on or off the lights of a vehicle.
In order to improve the safety and comfort of motor vehicles, many functions have been automated, thereby unburdening the driver. In one known method, the lights of the vehicle are automatically switched on and off as a function of brightness. Two light sensors are used: the first determines the brightness of the vehicle surroundings and switches on the lights of the vehicle as soon as the ambient brightness falls below a predetermined minimum brightness level. The second light sensor determines only the brightness in the driving direction and thus is able to determine whether the vehicle approaches a tunnel opening, e.g., in which case the second light sensor switches on the lights of the vehicle even though the ambient if brightness still exceeds the aforementioned minimum brightness level until the vehicle enters the tunnel. One disadvantage of this method is that short, dark sections are not recognized as such, so that the lights of the vehicle frequently switch on and then off again shortly thereafter, as is the case, for example, when driving beneath a bridge that spans the road. Drivers coming from the opposite direction may become annoyed; in any case, the service life of the gas discharge lamps is significantly reduced by these frequent switching processes.
The present invention is based on the object of making available a method and device, by which means the lights of a vehicle are reliably switched on if the ambient brightness is too low or if the vehicle enters a tunnel. Moreover, the lights of the vehicle are prevented from switching on and then off again a short time later when driving through short, dark sections.
According to the invention, this objective is realized with a method in which
the driving speed is determined,
the mean brightness H1 within a first cone that lies in front of the vehicle, looking into the driving direction, is determined, where the first cone has a large cone angle, and where the tip of the cone lies inside the vehicle,
the mean brightness H2 within a second cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the second cone is smaller than that of the first cone, and where the tip of the second cone lies inside the vehicle,
the mean brightness H3 within a third cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the third cone is smaller than that of the first cone, the tip of the third cone lies inside the vehicle, where the longitudinal axis of the third cone is elevated in the driving direction relative to the longitudinal axis of the second cone, as viewed from the side, and where the envelope of the third cone that lies outside its tip is located within the envelope of the first cone,
the lights of the vehicle are switched on if
the driving speed is greater than zero, and the brightness values H1, H2 and H3 fall below a minimum value Hmin,1 over a driving distance S1 
or
the driving speed is greater than zero, and the brightness value H2 is less than the brightness value H1 by an amount xcex94Hmin,1 and the brightness value H3 is greater than the brightness value H2 by less than an amount xcex94Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the brightness values H1, H2 and H3 fall below a minimum value Hmin,1 during a time interval xcex94Tmin,1, and
the lights of the vehicle are switched off if
the driving speed is greater than zero and the brightness values H1, H2 and H3 exceed a minimum value Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the brightness values H1, H2 and H3 exceed a minimum value Hmin,2 during a time interval xcex94Tmin,2.
The method according to the invention provides the advantage that the brightness ahead of the vehicle is also determined by the third light sensor oriented, when viewed from the side, at an inclination relative to the longitudinal axis of the second cone. The evaluation of this additional information in accordance with the proposed method makes it possible to differentiate, for example, the ceiling of a tunnel from the underside of a bridge that passes over a road. In the method according to the invention, the lights of the vehicle are switched on before the vehicle enters the tunnel, with the lights of the vehicle remaining switched off if the vehicle drives beneath a bridge that passes over a road. Since the driving distance S1 forms part of the switch-on and the switch-off condition, the speed of the vehicle is also taken into consideration. The method according to the invention also provides the advantage that the lights of the vehicle are only switched off if the brightness remains above a predetermined minimum level for a sufficient period of time.
According to the invention, the objective of the invention is also realized with a method in which
the driving speed is determined,
the mean brightness H1 within a first cone that lies in front of the vehicle, looking into the driving direction, is determined, where the first cone has a large cone angle, and where the tip of the cone lies inside the vehicle,
the mean brightness H2 within a second cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the second cone is smaller than that of the first cone, and where the tip of the second cone lies inside the vehicle,
the mean brightness H3 within a third cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the third cone is smaller than that of the first cone, where the tip of the third cone lies inside the vehicle, where the longitudinal axis of the third cone is elevated in the driving direction relative to the longitudinal axis of the second cone, as viewed from the side, and where the envelope of the third cone that lies outside its tip is located within the envelope of the first cone,
the lights of the vehicle are switched on if
the driving speed is greater than zero, and the mean values of the brightness values H1, H2 and H3 fall below a minimum value Hmin,1 over a driving distance S1 
or
the driving speed is greater than zero, and the mean value of the brightness value H2 is less than the mean value of the brightness value H1 by an amount xcex94Hmin,1 and the mean value of the brightness value H3 is greater than the mean value of the brightness value H2 by less than an amount xcex94Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the mean values of the brightness values H1, H2 and H3 fall below a minimum value Hmin,1 during a time interval xcex94Tmin,1, and
the lights of the vehicle are switched off if
the driving speed is greater than zero and the mean values of the brightness values H1, H2 and H3 exceed a minimum value Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the mean values of the brightness values H1, H2 and H3 exceed a minimum value Hmin,2 during a time interval xcex94Tmin,2.
This method provides the advantage that brief fluctuations of one or more brightness values do not cause the lights of the vehicle to be unnecessarily switched on and off. The speed of the vehicle is also taken into consideration by determining mean values while traveling a distance S1.
According to one variation of the method,
the driving speed is determined,
the mean brightness H1 within a first cone that lies in front of the vehicle, looking into the driving direction, is determined, where the first cone has a large cone angle, and the tip of the cone lies inside the vehicle,
the mean brightness H2 within a second cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the second cone is smaller than that of the first cone, and where the tip of the second cone lies inside the vehicle,
the mean brightness H3 within a third cone that lies in front of the vehicle, looking into the driving direction, is determined, where the cone angle of the third cone is smaller than that of the first cone, where the tip of the third cone lies inside the vehicle, where the longitudinal axis of the third cone is elevated in the driving direction relative to the longitudinal axis of the second cone, as viewed from the side, and where the envelope of the third cone that lies outside its tip is located within the envelope of the first cone,
the lights of the vehicle are switched on if
the driving speed is greater than zero, and the mean value formed by the brightness values H1, H2 and H3 falls below a minimum value Hmin,1 over a driving distance S1 
or
the driving speed is greater than zero and the mean value of the brightness value H2 is less than the mean value of the brightness value H1 by an amount xcex94Hmin,1 and the mean value of the brightness value H3 is greater than the mean value of the brightness value H2 by less than an amount xcex94Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the mean value formed by the brightness values H1, H2 and H3 falls below a minimum value Hmin,1 during a time interval xcex94Tmin,1, and
the lights of the vehicle are switched off if
the driving speed is greater than zero and the mean value formed by the brightness values H1, H2 and H3 exceeds a minimum value Hmin,2 over a driving distance S1 
or
the driving speed is equal to zero, the ignition is switched on and the mean value formed by the brightness values H1, H2 and H3 exceeds a minimum value Hmin,2 during a time interval xcex94Tmin,2.
This method according to the invention provides the advantage that the influence of xe2x80x9coutliersxe2x80x9d in the brightness values is additionally reduced due to the formation of a common mean value of the brightness values H1, H2 and H3.
According to another variant of the method according to the invention, the mean value formed by the brightness values H1, H2 and H3 is weighted, with the brightness value H1 given the heaviest weight, so that the influence of the brightness values H2 and H3 is reduced in comparison to H1 and the influence of the ambient brightness on the switching on or off of the vehicle lights is correspondingly increased.
The initially cited objective is also realized with a device for implementing the method according to the invention which contains a first light sensor for determining the mean brightness H1 of the light beams within a cone with a large cone angle, a second light sensor for determining the mean brightness H2 of the light beams within a cone with a small cone angle, where the envelope of the second cone, which is located beyond the tip, lies within the envelope of the first cone, a light control unit that switches the lights of the vehicle on and off in accordance with a method disclosed in one of the preceding claims, and a third light sensor for determining the mean brightness H3 of the light beams within a third cone with a small cone angle, where the envelope of the third cone, which is located beyond the tip, lies within the envelope of the first cone, and where the longitudinal axis of the third cone forms a small angle with the longitudinal axis of the second cone.
This device provides the advantages that an additional brightness value is determined that is absolutely imperative for reliably switching the vehicle lights on and off, and that the light control unit switches the lights of the vehicle on and off in accordance with a method disclosed in one of the preceding claims.
According to one advantageous embodiment of the invention, the cone angle of the first cone is greater than 10xc2x0, so that a sufficiently large portion of the ambient light is used for determining the brightness value H1.
According to another advantageous embodiment of the invention, the cone angle of the first cone is 28xc2x0, so that a certain selected portion of the ambient light is used for determining the brightness value H1.
According to another advantageous embodiment of the invention, the cone angle of the second and/or third cone is less than 5xc2x0, in particular, 1.2xc2x0, so that a directional or nearly point-wise determination of the brightness values H2 and/or H3 takes place.
In another embodiment of the invention, the longitudinal axes of the first and the second cone extend parallel to one another. In this case, it is advantageous that the light sensors be arranged parallel to one another.
In another embodiment, the angle between the longitudinal axes of the second and the third cone is less than 5xc2x0, so that the brightness value H3 decreases long before the vehicle enters a tunnel or passes beneath a bridge.
According to another advantageous embodiment of the invention, xcex94Hmin,1 is the product of a factor between zero and one and the brightness value H1, such that the ambient brightness influences the switching on of the vehicle lights. In this way, the differences in brightness between a clear summer day and a cloudy winter day can be taken into consideration.
According to another advantageous embodiment of the invention, xcex94Hmin,2 is the product of a factor between zero and one and the brightness value H2, such that the brightness of a region which lies in front of the vehicle influences the switching on of the vehicle lights.
According to another advantageous embodiment of the invention, the brightness value Hmin,1 and the brightness value Hmin,2 can be freely selected such that the user of the device is able to adapt the switching on or off of the vehicle lights to individual requirements.
According to another advantageous embodiment of the invention, the brightness values H1, H2 and H3 are evaluated during a time interval xcex94T such that the data quantity is reduced and the method according to the invention can be carried out more easily.
The initially cited objective is also realized with a vehicle equipped with a device according to the invention, in which the longitudinal axes of the first and second cone extend in the direction of the longitudinal axis of the vehicle, and in which the longitudinal axis of the third cone extends in the direction of the longitudinal axis of the vehicle as seen from above.
This vehicle provides the advantages that the device according to the invention can be securely connected to the vehicle and that a high operational reliability is ensured.
According to another advantageous embodiment of the invention, the longitudinal axes of the first and the second cone extend in the driving direction of the vehicle, and the longitudinal axis of the third cone extends in the driving direction, as seen from above, such that the brightness in the driving direction can be determined. This is advantageous on tortuous roads, particularly if a tunnel entrance or exit lies on a curve.
According to another variant, the longitudinal axes of the first and the second cone extend in the steering direction of the front wheels, and the longitudinal axis of the third cone extends in the steering direction of the front wheels, as seen from above, such that the device according to the invention can be easily and inexpensively adjusted when the driving direction of the vehicle changes.
According to another advantageous embodiment of the invention, the longitudinal axes of the first, second and third cones can be freely selected such that the device can be adapted, for example, to different load conditions or asymmetric vehicles.